1. Technical Field
The present disclosure relates generally to radio frequency integrated circuits, and more particularly, to wide dynamic range broadband current mode linear detector circuits for high power radio frequency power amplifiers.
2. Related Art
Wireless communications systems are utilized in a variety contexts involving information transfer over long and short distances alike, and a wide range of modalities for addressing the particular needs of each being known in the art. As a general matter, wireless communications involve a radio frequency (RF) carrier signal that is variously modulated to represent information/data, and the encoding, modulation, transmission, reception, de-modulation, and decoding of the signal conform to a set of standards for coordination of the same.
Many different mobile communication technologies or air interfaces exist, including GSM (Global System for Mobile Communications), EDGE (Enhanced Data rates for GSM Evolution), and UMTS (Universal Mobile Telecommunications System). Various generations of these technologies exist and are deployed in phases, with one common third generation (3G) UMTS-related modality referred to as UMTS-FDD (frequency division duplexing) being W-CDMA (Wideband Code Division Multiplexing). More recently, 4G (fourth generation) technologies such as LTE (Long Term Evolution), which is based on the earlier GSM and UMTS standards, are being deployed. Besides mobile communications modalities such as these, various communications devices incorporate local area data networking modalities such as Wireless LAN (WLAN)/WiFi. Along these lines, last-mile wireless broadband access technologies such as WiMAX (Worldwide Interoperability for Microwave Access) are also being implemented.
A fundamental component of any wireless communications system is the transceiver, that is, the combined transmitter and receiver circuitry. The transceiver encodes the data as a baseband signal and modulates the baseband signal with an RF carrier signal. Upon receipt, the transceiver down-converts the RF signal, demodulates the baseband signal, and decodes the data represented by the baseband signal. An antenna connected to the transmitter converts the electrical signals to electromagnetic waves, and an antenna connected to the receiver converts the electromagnetic waves back to electrical signals. Depending on the particulars of the communications modality, single or multiple antennas may be utilized.
Transceivers typically do not generate sufficient power or have sufficient sensitivity for reliable communications standing alone. Thus, additional conditioning of the RF signal is necessary. The circuitry between the transceiver and the antenna that provide this functionality is referred to as the front end, which is understood to include a power amplifier for increased transmission power, and/or a low noise amplifier for increased reception sensitivity. Additionally, there may be a RF switch that selectively connects the transmit chain (including the power amplifier), and the receive chain (including the low noise amplifier) tot the antenna. Each band or operating frequency of the communications system may have a dedicated power amplifier and low noise amplifier tuned specifically to that operating frequency.
Detecting and controlling the performance of an amplifier makes it possible to maximize the output power while achieving optimum linearity and efficiency, and so a power detector may be integrated into the front end circuit. The power detector is typically utilized in the transmit chain to monitor the output of the power amplifier, and generates a direct current (DC) voltage that is related to the measured power. This voltage is fed back to the transceiver, which uses it for signal strength indication. In turn, the proper gain may be set in a variable gain amplifier. A directional coupler may be connected to the output of the power amplifier, with one of its ports being connected to the input of the power detector.
In order to achieve higher output power, the size of the amplifier circuit, and in particular the transistors therefor, must be increased for optimal drain impedance, current handling capacity, and heat dissipation. The higher output power from the amplifier also impacts the power detector, as a wide dynamic range is needed for detecting both low and high output power with monotonically increasing voltage. Yet, the push for ever-decreasing size in mobile communications devices is at odds with larger integrated circuit components needed for handling higher power levels and incorporating more features.
Power detectors generally fall into one of two types—diode-based and logarithmic-based. There are several shortcomings with respect to conventional diode-based power detector circuits. Namely, the output voltage versus output power tends to follow a parabolic curve. Such power detectors also have narrow dynamic range and lack sufficient linearity across the entire output power range. In some cases, a complicated algorithm for baseband calibration is needed. A logarithmic power detector can be linear across a wider power detection range, but in order to achieve this, multiple cascaded attenuation and amplification stages with a final summation amplifier is necessary. Furthermore, the circuitry is complicated, and accordingly occupies a large footprint on the integrated circuit die. The logarithmic power detector also has a significantly higher current consumption for the wider power detection range, which adds to the challenges of achieving high power-added efficiency (PAE) of the overall power amplifier circuit.
Accordingly, there is a need in the art for an improved non-logarithmic power detector with wide dynamic range. Additionally, there is a need for power detectors with minimal physical size, and capable of operation with a variety of wireless communication modalities and the different signal types thereof.